Vim autoindent Tabs and Spaces - Editors

Okay, I know there have been a million questions regarding tabs vs.
spaces. I have done a ton of searches to find the answer to my
question, and I haven't managed to find one. I want to properly mix
tabs and spaces in my indentation, but vim does not seem to allow me to
do this, at least not with my current settings. I am sure there is some
obscure option to change, but I can't figure out what.

I do not want to discuss proper indentation (tabs vs. spaces), but I
will review my scheme to put my question in the proper frame. I use
tabs to indicate indentation level, and I used spaces to properly align
multi-line statements. With this in mind, anyone should be able to view
my source code with any tabstop setting and get proper code alignment.
This most applies to C code, but has also cropped up in some Python and
Perl usage. In my example below, I have used ^I to indicate tabs and .
to indicate spaces. It might not look right if you are not viewing this
with a fixed width font.

int main (int argc, char** argv) {
^Iint i = 1;
^Iif (i) {
^I^IsomeReallyLongFunction(with, a, lot, of, wordy, arguments, and,
^I^I......................."perhaps maybe a quoted string",
^I^I......................."and one more quoted string");
^I}
^Ireturn 0;
}

My current .vimrc is:

set noexpandtab
set tabstop=4
set shiftwidth=4

The problem is that when vim auto-indents the 3rd line of my function
call, it converts every 4 spaces into a tab character. It looks fine as
I'm editing it, but if I later check out the file using a different tab
width (i.e. with cat or less on default settings), the 3rd line of the
call is not lined up with the 2nd.

I simply want vim to exactly copy my indentation of the previous line,
without converting anything. What can I change to do this? Even if I
have to write something crazy in my .vimrc, I'm cool with that, because
it will save me a lot of hassle in the long run.

Note: I am only using the default indent feature currently (I believe
it's smartindent). I do not mind typing a simple Tab when I want to
indent, or typing multiple spaces to align multi-line function calls. I
simply want vim to exactly copy my previous indentation when continuing
to the next line.

Thanks in advance,
Brandon